122 NASSIN^. 



Sub-gen. tritia, Risso (PlanaxiS; Elsso, not Lmn.). 



Spire elevated, whorls reticulated ; inner lip smooth, with the 

 callus moderate ; outer lip simple, not variced or denticulate. 



cancellata, Cheni. glauca, C. B. Adams. 



Cooperi, Forbes. obsoleta, Say. 



costellifera, A. Adams. Panamensis, C. B. Adams. 



dealbata, A . Adams. reticulata, Liiin. 



fossata, Gould. trivittata, Say. 



Gayii, Kien. Woodwardi, Forbes. 



Genus NERITULA, Plancus. 



Shell ovate, depressed, axis distorted ; spire flattened, 

 oblique, whorls smooth ; aperture depressed ; columella 

 smooth ; inner lip callous, spread over the body- whorl ; 

 outer lip reflected, not denticulate or striated. 



S^n. Cyclops, Montf. Cyclope, Risso. Nana, 5, 8chum. 

 Nanina, Risso. Cyclonassa, Swains. Cyclocyrtia, Agass. 



Ex. N. neritea, Xmw^MS, pL 12, fig. 8. Shell, N. neritea, 

 fig. 8, a. 



In Neritula the last whorl is depressed and extends 

 over the penultimate whorl, nearly covering and conceal- 

 ing the spire, which, consequently, appears very obtuse. 

 The animal has a bifid tail similar to that of Nassa, 



Species of Neritula. 

 neritea, Linn. pellucida, Risso. 



Genus TEINOSTOMA, H. and A. Adams. 

 Shell orbicular, depressed, subspiral, polished, last whorl 



